Electrical and chemical stability engineering of solution-processed indium zinc oxide thin film transistors via a synergistic approach of annealing duration and self-combustion process

The electrical and chemical stability of solution-processed indium zinc oxide (IZO) channel thin-film transistors (TFTs) were engineered via a synergistic approach of annealing duration and self-combustion process. In particular, the amorphous IZO TFTs that were thermally treated at 400 °C for 3 h using the specific precursor combination to generate internal self-combustion energy showed the best electrical performance [high saturation mobility (μ_SAT)=2.7 cm²/V s] and stability [low threshold voltage shift (ΔV_TH) under positive bias stress of 10.5 V] owing to the formation of oxide films with excellent metal–oxide–metal (M–O–M) bonds, fewer impurities, and an amorphous phase compared to IZO TFTs using other precursor formulas and annealing times. Longer annealing times led to a saturated M–O bond ratio and crystallization via extreme thermal annealing, which induced electrical degradation (low μ_SAT and high ΔV_TH) of IZO TFTs. In the wet chemical patterning of electrodes, conventional acidic and basic wet etchants cause severe damage to the surfaces of the IZO channels; thus, insufficiently annealed IZO TFTs exhibited considerable degradation in terms of their on-current level and mobility. Alternatively, the TFTs subjected to an excessively long-term thermal annealing showed only a moderate decrease in mobility with the formation of small nanocrystals.     

Effect of annealing protection atmosphere on the ferroelectric yttrium doped hafnium oxide thin films

The 10 nm thick yttrium doped hafnium oxide (Y:HfO₂) thin films, prepared by chemical solution deposition which using all-inorganic aqueous salt reagents, were fabricated on Si (100) substrates. The crystalline structure, chemical composition and ferroelectric properties of thin films, annealed in protection atmosphere of Air, Ar and N₂, were examined. Result showed that the crystalline structure and ferroelectric properties of films exhibited a strong annealing protection atmosphere dependence. When compared to annealing protection atmosphere of Air and Ar, the films with the N₂ exhibited lowest m-phase fraction of 19.4%, and the highest oxygen vacancy percentage content of 3.06%, accompanied with the highest relative permittivity of 50.9 and the remanent polarization of 14.6 μC/cm². These excellent ferroelectric properties were correlated with asymmetric orthorhombic phase and the concentration of oxygen vacancy introduced from the nitrogen doping concentration.     

Effect of heat treatment atmosphere on the piezoresistivity of indium tin oxide ceramic strain sensor

Indium tin oxide (ITO) strain sensors were prepared by RF magnetron sputtering, and then heat treated in nitrogen and air atmosphere, respectively. The effect of air and N₂ heat treatment on the piezoresistivity of ITO ceramic strain sensors were investigated at 1200 °C. It was found that although both the ITO ceramic strain sensors heat treated in N₂ and air had similar temperature coefficient of resistance (TCR), the ITO strain sensor heat treated in N₂ had better resistance stability. In addition, the ITO strain sensor heat treated in N₂ had a smaller but more stable gage factor, compared to that in air. These observations were attributed to the increased content of Sn⁴⁺ donors and the enhanced photon scattering due to smaller grain sizes after the incorporation of nitrogen into ITO lattice.     

Enhancing the temperature coefficient of resistance of Pt thin film resistance-temperature-detector by short-time annealing

In this work, we report the influence of annealing time on the electrical properties of Pt thin film resistance-temperature-detectors (RTD) with Ti adhesion layers. It is found that the temperature coefficient of resistance (TCR) of the Pt thin film RTD strongly depends on the air annealing time. Increasing the annealing durations from 1, 3, 10 to 60 min at 900 °C, the TCR tends to rise up firstly, and then drops down. A maximum TCR of 3.2 × 10⁻³/°C at 25 °C is achieved in the RTD annealed for 3 min, which is larger than most of other reported values. It is believed that the annealing time of 3 min may be sufficient to enlarge the grain size and to reduce the lattice defects, giving rise to the maximum TCR by decreasing the resistance at 25 °C. On the contrary, prolonging the annealing duration causes the interdiffusion and oxidation Ti significantly, which has been clearly evidenced by the depth analyses of X-ray photoelectron spectroscopy. Such interdiffusion and oxidation of Ti reduces the TCR by increasing the resistance.     

Seed-mediated electrochemical growth of gold nanostructures on indium tin oxide thin films

Two-dimensional gold nanostructures (Au NSs) were fabricated on amine-terminated indium tin oxide (ITO) thin films using constant potential electrolysis. By controlling the deposition time and by choosing the appropriate ITO surface, Au NSs with different shapes were generated. When Au NSs were formed directly on aminosilane-modified ITO, the surface roughness of the interface was largely enhanced. Modification of such Au NSs with n-tetradecanethiol resulted in a highly hydrophobic interface with a water contact angle of 144°. Aminosilane-modified ITO films further modified with colloidal Au seeds before electrochemical Au NSs formation demonstrated interesting optical properties. Depending on the deposition time, surface colors ranging from pale pink to beatgold-like were observed. The optical properties and the chemical stability of the interfaces were characterized using UV-vis absorption spectroscopy. Well-defined localized surface plasmon resonance signals were recorded on Au-seeded interfaces with λ_max = 675 ± 2 nm (deposition time 180 s). The prepared interfaces exhibited long-term stability in various solvents and responded linearly to changes in the corresponding refractive indices.     

Effect of heat treatment on the dispersion and sintering behaviour of tin doped indium oxide powders

Due to the importance of structural uniformity of ITO targets on the properties of ITO films, the untreated and heat treated tin doped indium oxide powders were used to study the effects of four different dispersants on the dispersion behaviour of nanosized ITO powders. The optimum dispersant is NH₄PAA and its optimum amount is 1.00?wt% when the pH value is 9.0. In addition, the effect of the treatment temperature of nanosized ITO powders on the dispersion and sintering behaviour was also studied by SEM, TEM and XRD. The solid loading of ITO slurries and the relative density of the sintered bodies prepared with ITO powders treated at 900?°C could reach 40?vol% (untreated, 25?vol%) and 98.53% (untreated, 95.04%), respectively. The results indicate that the heat treatment of powders at 900?°C allowed obtaining powders from which ITO aqueous suspensions with high solid loading could be prepared and dense bodies after sintering. In another word, the appropriate heat treatment process for tin doped indium oxide powders could reduce the sintering temperature by 50?℃ and refine the grain size.     

Transformation of sputtered calcium copper titanate thin film into nanorods by sequential annealing

Rapid synthesis of long calcium copper titanate (CCTO) nanorods was carried out by sequential annealing. CCTO thin films have been deposited on p-Si substrate by RF sputtering technique and afterwards, the samples were thermally treated using a preheated furnace by varying the annealing temperature from 850 °C to 1100 °C. CCTO nanorods of 12 µm lengths and 400–600 nm diameters were synthesized at 1100 °C. Based on the FESEM observations, a plausible growth mechanism has been proposed to explain the formation of nanorods. The (220) XRD peak of the CCTO film became prominent for the annealing temperature of 950 °C. The presence of nanoscale crystals in amorphous matrix has been observed by HRTEM studies. The elemental mapping of CCTO nanorod has shown a spatial variation of elements throughout the nanorod. The oxide and interface charge density was found to be increased with the rise in annealing temperature.     

Fast switching electrochromism from colloidal indium tin oxide in tungstate-based thin film assemblies

Layer-by-layer assembly was used to alternately deposit tungstate anions with cationic poly(4-vinylpyridine-co-styrene) to generate electrochromic thin films that transit from transparent to dark blue in their oxidized and reduced states, respectively. Tungstate is a good electrochromic material because it is completely colorless in its deposited state, while most other electrochromic materials exhibit some type of color in the absence of an applied voltage. Despite its advantages, tungstates are plagued by long switching time (>30 s), which is common amongst ceramic electrochromics, due to lack of electrical conductivity in at least one of the two states. In an effort to decrease switching time, indium tin oxide (ITO) nanoparticles were incorporated into these tungstate-based assemblies. In the absence of ITO, these films take 30-60 s to completely switch and exhibit reduced contrast with each switch. ITO-containing films, with ITO in every other bilayer, fully switch in 14 s and do not exhibit the same drift in transmittance with repeated switching. ITO allows these films to maintain electrical conductivity in both states, which is the source of this faster, more stable switching. With further optimization, this combination of fast switching and high contrast makes these films promising for use in smart windows and flexible displays.     

A leaf-like structured ITO conductive transparent thin film from visible to near-infrared region with enhanced stability

ITO thin films as the optical and electrical windows to transform photons and charges have been applied in many areas. Here, a leaf-like structured particle is composed of small particles growing along three different orientations leading to low thermal stress accompanied by well transmittance (85%) in a wide wavelength range from visible to near-infrared region and a narrowed band gap 3.07 eV. The evolution of structure and electronic performance was studied to obtain the low resistivity (12 μΩ m) and enhanced stability of the film (1000 °C). The leaf-like structure can be maintained under 600 ℃ and the electrical properties can be modified in He and N₂ atmosphere, owing to the reduced defects, increased concentration of Sn and carrier mobility. Although the structure has changed after being annealed at 1000 °C in N₂, the thin film performs excellent electrical properties (?3.44 × 10²⁰ cm^?3 and 28 cm² V^?1 s^?1).     

Highly ordered columnar ITO thin film with enhanced thermoelectric and mechanical performance over wide temperature range

Indium tin oxide (ITO) based thin films offer the possibility to improve the performance of high-temperature thermocouples by providing good sensitivity and reliability over a wide temperature range. In this study, a thin but robust ITO-based thin-film thermocouple, with a low-crystallised highly ordered columnar structure, was fabricated. The electrical conductivity exhibited a high temperature-dependent sensitivity owing to the increasing density with increasing temperature. The nano-hardness and interfacial robustness were evaluated and found to exhibit excellent service reliability at high temperatures because of the low thermal stress. Furthermore, the similar mechanical and electrical performances of the thin films, after annealing at 600 and 800 °C, demonstrated that the enhanced performance was mainly determined by the orientation of the ITO thin films. An enhanced Seebeck coefficient (～100 μV K^?1) was obtained for the ITO thin film after annealing at 1000 °C, resulting in a special structure with profuse nanoholes. These results highlight the good mechanical performance and stability of the thermoelectric properties of highly ordered columnar thin films over a wide temperature range, and can serve as a guide for the preparation of thin but robust functional ceramic-based materials.     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Photocatalytic properties of visible-light enabling layered titanium oxide/tin indium oxide films

Visible-light enabling titanium oxide/tin indium oxide (TiO₂/ITO) thin films deposited on unheated glass slides with prolonged deposition duration were investigated in this study. Structural properties characterized by X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) showed typical polycrystalline structure with primary anatase phase along with elongated pyramid-like grains lying on the film surface and densely packed columnar structure from cross-sectional profile. The XRD preferential peak of (2 1 1) and the Raman peak intensity at 640 cm⁻¹ dramatically increased without noticeable broadening and shift as the deposition time was prolonged beyond 2 h. This implies that more perfectly crystalline structure, less internal stress, and comparatively larger grains were obtained by this technique. The Ti2p_3/2 and O1s XPS peaks shifted toward higher binding energy suggest that the local chemical state was influenced by the prolonged deposition duration in the film, which resulted in red shift of absorption threshold into visible-light region. Under ultra-violet (UV) and visible-light illumination, the visible-light enabling film exhibited the best photocatalytic activity on MB degradation with the rate-constant of about 0.231 h⁻¹. Hydrophilic conversion rate was estimated to be 8.14 × 10⁻³ deg⁻¹ min⁻¹ and long-term UV-induced hydrophilicity of 10° in the dark storage up to 72 h was observed. In addition to its inherent characteristics of the layered TiO₂/ITO structure on hole/electron separation, all these could be attributed to more perfectly formed crystalline structure, densely packed columnar crystals and the surface roughness along with its enlarged surface area.     

Surface scattering mechanisms of tantalum nitride thin film resistor

In this letter, we utilize an electrical analysis method to develop a TaN thin film resistor with a stricter spec and near-zero temperature coefficient of resistance (TCR) for car-used electronic applications. Simultaneously, we also propose a physical mechanism mode to explain the origin of near-zero TCR for the TaN thin film resistor (TFR). Through current fitting, the carrier conduction mechanism of the TaN TFR changes from hopping to surface scattering and finally to ohmic conduction for different TaN TFRs with different TaN microstructures. Experimental data of current–voltage measurement under successive increasing temperature confirm the conduction mechanism transition. A model of TaN grain boundary isolation ability is eventually proposed to influence the carrier transport in the TaN thin film resistor, which causes different current conduction mechanisms.     

High-temperature thin film lithium niobium oxide transducers for bolts

In the present work, we studied structure, surface morphology, and ultrasonic response of thin film Lithium Niobium Oxide (LNO) transducers deposited on Inconel bolts, stainless steel and silicon substrates by radio frequency magnetron sputtering. The deposited transducer material was a mixture of LiNbO₃/LiNb₃O₈ phases, having a well-developed columnar structure. Further, the in-situ high-temperature ultrasonic response was studied in the temperature range of 18–800 °C in ambient air during short-term annealing. It was observed that long-term annealing (at 700 °C for 160 h and 800 °C for 40 h) deteriorated the ultrasonic response, owing to the irreversible change from the initial columnar structure to the porous granular structure. Dielectric and piezoelectric properties of the thin film LNO transducers were also studied. The thin film LNO ultrasonic transducers have potential applications in bolts and screws up to 700 °C.     

Effect of rapid thermal annealing on the properties of zinc tin oxide films prepared by plasma-enhanced atomic layer deposition

The effect of rapid thermal annealing treatments on the microstructure, surface morphology, and optical characteristics of zinc tin oxide (ZTO) films produced by plasma-enhanced atomic layer deposition was investigated. The ZTO films were annealed in oxygen atmosphere for 2 min at four selected temperatures from 500 to 800 °C. The X-ray diffraction showed that the annealing temperature has a great influence on the crystalline characteristics of ZTO films. The film shows complete amorphous structure for as-deposited ZTO film. Meanwhile, the spinel zinc stannate Zn₂SnO₄ was obtained for the samples annealed from 500 to 800 °C, which shows polycrystalline nature. The X-ray photoelectron spectroscopy proved that the annealing process in oxygen gas can effectively can reduce the oxygen vacancy defects in the films. In addition, the photoluminescence spectroscopy manifests an ultraviolet emission with a broad peak range from 345 to 385 nm. Moreover, the ultraviolet luminescence intensity increases continuously with the increase of annealing temperature. Spectroscopic ellipsometry analyses demonstrate that the refractive index of annealed films increases as the increase of annealing temperature, while the extinction coefficient decreases gradually with the increase of annealing temperature in the visible light range.     

Indium tin oxide exhibiting high poly-crystallinity on oxygen plasma-treated polyethylene terephthalate surface

Low-resistivity indium tin oxide [ITO] film was successfully deposited on oxygen plasma-treated polyethylene terephthalate [PET] surfaces at room temperature. X-ray diffraction [XRD] measurements demonstrated that the film deposited on the PET surface that had not been treated with oxygen plasma had an amorphous structure. In contrast, after the low-power oxygen plasma treatment of the PET surface, the ITO film deposited on the PET surface had a poly-crystalline structure due to interactions between electric dipoles on the PET surface and electric dipoles in the ITO film. The minimum resistivity of the poly-crystalline ITO was about 3.6 times lower than that of the amorphous ITO film. In addition, we found that the resistivity of ITO film is proportional to the intensity of the (400) line in the film''s XRD spectra.     

Focus on the ferroelectric polarization behavior of four-layered Aurivillius multiferroic thin film

The well-saturated ferroelectric hysteresis loops with double remnant polarization up to 50?μC/cm² were obtained in four layered Aurivillius-type multiferroic Bi₅FeTi₃O₁₅ thin film. Pulsed positive-up negative-down polarization measurements demonstrate the intrinsic ferroelectric polarization, which present optimal rectangularity and polarization value. The hysteresis loops measurements with larger frequency range of 0.2–100?kHz indicate stable and ultra-fast switching speed of ferroelectric domains. Persistent retention properties were observed, and they are also independent of the applied electric field. In fatigue test an increased dielectric constant is observed along with the suppression of switchable polarization. Both of them can be restored partly to their original values via the stimulating of high electric field. The block domain switching due to the oxygen vacancies aggregated on domain walls are discussed for those characteristics. It is providing important contributions of domain wall pinning in the polarization degradation of Aurivillius-type ferroelectric films with four layers.     

Rapid thermal annealing effect of transparent ITO source and drain electrode for transparent thin film transistors

We investigated the rapid thermal annealing (RTA) sequence effect on the electrical, optical, morphological, and structural properties of transparent thin film transistors (TTFTs) with an indium gallium zinc oxide (IGZO) channel and an indium tin oxide (ITO) source/drain. The electrical and optical properties of the IGZO channel and the ITO source/drain electrodes were compared as a function of RTA temperature in ambient air. The performance of a TTFT with only an RTA-processed IGZO channel was compared with that of a TTFT with an RTA-processed IGZO channel and ITO source/drain electrodes. Using the circular transmission line measurement (CTLM) method, we suggest a possible mechanism that explains the effect of the RTA process on the performance of the TTFT with only an annealed IGZO channel vs. that with an annealed IGZO/ITO multilayer. The TTFT with an RTA-processed IGZO/ITO multilayer showed a threshold voltage shift, an improved on/off ratio of 3.54 × 10¹¹, a subthreshold swing of 0.33 V/decade, and a high mobility of 8.69 cm²/V·s. This indicates that simultaneous RTA processing for an IGZO channel and an ITO electrode is beneficial for the fabrication of high-performance TTFTs.     

Effect of stabilizer on synthesis of indium tin oxide nanoparticles

Indium tin oxide nanoparticles with shapes varying from sphere to cubic were synthesized by controlling the ratio of the concentrations of the protective polymer (PVP) to indium tin oxide precursor in their preparation by co-precipitation. Transmission electron microscopy was used to determine the size and shape. The XPS spectra of the particles revealed that the atomic ratios of In:Sn and (In + Sn):O are 10.0:1.0 and 1.0:1.5, respectively for both of the spheres and the cubes. X-ray diffraction study showed that these particles have the same crystalline structure. Thus, it is shown that the formation of the various shapes of the ITO particles could be achieved by using different ratios of protective polymer instead of varying the protective polymer or the sintering process.     

Investigation of large Seebeck effect by charge mobility engineering in CuAlO2 thin films grown on Si substrate by thermal evaporation

In this research paper, we have reported giant enhancement in Seebeck coefficient of AlCuO₂ thin films by charge mobility engineering. Thin films of AlCuO₂ were grown by the evaporation of Al and Cu powder in tube furnace on Si (100) substrate. The experimental conditions were sets as; tube pressure (0.2?Torr), source to substrate distance (3?cm), evaporation temperature (1000?°C), oxygen flow rate (60?sccm) and evaporation time was (30?min). The charge mobility and diffusion of oxygen atoms were controlled by annealing the grown samples in oxygen environment at various temperatures from 600 to 800?°C with a step of 100?°C for one hour in muffle furnace. The observed giant enhancement in Seebeck coefficient (150–1050?μV/K) can be explained as; The annealing generates oxygen interstitials and causes the charge scattering mechanism shift from lattice to impurity scattering mechanism. In the impurity scattering mechanism, mobility of charge carriers increased with temperature. This increase in mobility results in the giant enhancement of Seebeck coefficient. The argument was verified by Hall data which suggested that concentration of oxygen interstitials increased by annealing temperature. To further strengthened our argument we have performed XRD and FTIR measurements. XRD data has showed that as grown sample consists of one peak at angle 32° related to (006) phase of CuAlO₂. Annealing resulted in the generation of new phases at angles 35°, 42.5° and 48.4° which were related to CuO (111), CuAlO₂ (104) and CuAlO₂ (009) respectively. FTIR spectrum verified the presence of Cu-O and Al-O at wavenumbers 450?cm^?1 and 600?cm^?1 respectively.